1. Field of the Invention
The present invention relates to devices connected to an IEEE1394 serial bus via an IEEE1394 digital interface board, and in particular, to a receiving device such as a printer, which consistently establishes a point-to-point connection with a sending device on the bus and receives data from the sending device by isochronous transfer.
2. Description of the Related Art
Conventionally, a receiving device such as a printer, which consistently establishes a point-to-point connection with a sending device on an IEEE1394 serial bus (hereinafter abbreviated to the bus) and receives data from the sending device by isochronous transfer, exists among the devices connected to the bus. When transmitting data to this kind of receiving device, the sending device normally executes the acquisition and release of the resources of a band and so forth for the isochronous data transfer at the time of starting and stopping isochronous data transfer.
Next, resources acquisition processing and resources release processing by the sending device will be described with reference to FIG. 7. When executing the isochronous data transfer with the receiving device such as a printer connected by the point-to-point connection, the sending device acquires resources of a band and a channel for the isochronous data transfer when starting the isochronous data transfer to the receiving device (YES at S101) and executes the actual isochronous data transfer (S103) after the above resources acquisition is successfully achieved (S102). When stopping the isochronous data transfer (S104), the acquired resources are released. If the resources release is successfully achieved (S105), the sending device can reacquire the resources of the band and so forth for the isochronous data transfer when the isochronous data transfer from the sending device to the receiving device is restarted, and therefore, the isochronous data transfer can be correctly achieved.
However, according to the aforementioned conventional system in which the sending device executes the acquisition and release of the resources of the band and the channel for the isochronous data transfer every time the sending device executes the isochronous data transfer by the point-to-point connection, when the sending device fails in releasing the resources at the time of stopping the isochronous data transfer due to a bug of a program or the like as shown in FIG. 8 (YES at S115), some troubles mentioned below are possible to happen. To be concrete, at the time of restarting the isochronous data transfer to the receiving device (YES at S116), there is a possibility that the sending device cannot reacquire the band for the isochronous data transfer as a consequence of a shortage in the band, and a possibility that the sending device cannot reacquire the resources of an identical channel that the sending device released (S117). Accordingly, there is a possibility that the isochronous data transfer becomes unable to be executed between the sending device and the receiving device.